Acanthamoeba keratitis is a debilitating infection of the cornea. At present, diagnosis of the disease is not straightforward and treatment is problematic, consisting of hourly, around the clock, topical application of a combination of drugs for an extended period of time. Despite the aggressive treatment, recrudescence may occur. In view of the devastating nature of the disease and the problems associated with the therapy, our goals are to find a means to identify individuals who are at risk and provide them with rationally designed strategies to protect against the infection. The adhesion of the parasite to the host cells is the critical first step in the pathogenesis of infection. During the previous funding period, we demonstrated that Acanthamoebae express a mannose receptor which mediates adhesion of the amoeba to corneal epithelial cells. For an understanding of the mechanism by which the mannose-mediated adhesion of the amoeba to host cells triggers events which ultimately kill the host cells, in Aim 1, we shall clone a cDNA encoding the amoeba mannose receptor and will establish whether the mannose receptor is a transmembrane protein with potential for modulating signal transduction events. In Aim 2, we shall determine whether oral immunization of hamsters with specifically the carbohydrate recognition domain of the amoeba mannose receptor leads to an elevated antibody level in their tears, and, if so, whether the immune response provides protection against the infection. We have recently shown that subsequent to the mannose-mediated adhesion of the amoeba to host cells, a specific proteinase, P3, is secreted into the co-culture media. Studies proposed in Aim 3 are to test a hypothesis that P3 may be an important player in the cascade of contact-dependent events involved in the amoeba-induced cytolysis of corneal epithelial cells. It is hoped that this study will contribute to a better understanding of the molecular basis of Acanthamoeba keratitis and will ultimately improve the prospects of preventing the disease. In addition, this study will contribute to the basic understanding of the pathogenic mechanisms and cell biology of infections in general and as such, benefit future investigators looking to prevent ocular infections caused by other pathogens.